This program, under the direction of Dr. Morton Lippmann, includes eighteen active projects being conducted by five full-time and three part-time members. The primary objective of this research program is to improve the scientific basis and techniques for assessing human exposure, and to apply state-of-the-art knowledge for establishing direct relationships among human exposure to environmental toxicants, resulting doses to target sites, and their directly measurable health outcomes. A range of activities, extending from air sampling and analytical methods development to in-vivo retention measurements and micro-environmental modeling is included. The factors determining internal dose from inhaled toxicants are investigated through studies of regional and intrabronchial particle and vapor deposition and clearance, and through studies in radionuclide metabolism. Field studies are also being conducted of exposure-response relationships in natural populations, especially those involving ambient air exposures and physiological and symptomatic responses.